Abstract
Behaviorally-relevant sounds such as conspecific vocalizations are often available for only a brief amount of time; thus, goal-directed behavior frequently depends on auditory short-term memory (STM). Despite its ecological significance, the neural processes underlying auditory STM remain poorly understood. To investigate the role of the auditory cortex in STM, single- and multi-unit activity was recorded from the primary auditory cortex (A1) of two monkeys performing an auditory STM task using simple and complex sounds. Each trial consisted of a sample and test stimulus separated by a 5-s retention interval. A brief wait period followed the test stimulus, after which subjects pressed a button if the sounds were identical (match trials) or withheld button presses if they were different (non-match trials). A number of units exhibited significant changes in firing rate for portions of the retention interval, although these changes were rarely sustained. Instead, they were most frequently observed during the early and late portions of the retention interval, with inhibition being observed more frequently than excitation. At the population level, responses elicited on match trials were briefly suppressed early in the sound period relative to non-match trials. However, during the latter portion of the sound, firing rates increased significantly for match trials and remained elevated throughout the wait period. Related patterns of activity were observed in prior experiments from our lab in the dorsal temporal pole (dTP) and prefrontal cortex (PFC) of the same animals. The data suggest that early match suppression occurs in both A1 and the dTP, whereas later match enhancement occurs first in the PFC, followed by A1 and later in dTP. Because match enhancement occurs first in the PFC, we speculate that enhancement observed in A1 and dTP may reflect top–down feedback. Overall, our findings suggest that A1 forms part of the larger neural system recruited during auditory STM.
Highlights
One of the vital cognitive processes enabling adaptive behaviors in humans and other animals is short-term memory (STM), i.e., the temporary retention of behaviorally-relevant information in the absence of direct stimulation (Goldman-Rakic, 1995)
BEHAVIORAL RESULTS The subjects attained, on average, 65.5% overall accuracy based on 75 total behavioral sessions. This modest level of accuracy is common for non-human primates performing auditory STM tasks, even after extensive training (Fritz et al, 2005; Scott et al, 2012, 2013; Bigelow and Poremba, 2013a, 2014)
Relatively poor compared to studies of visual STM in monkeys (e.g., Fritz et al, 2005), a comparison of the number of correct and incorrect trials per session confirmed that performance was well above chance [F(1, 74) = 315.1, p < 0.05)
Summary
One of the vital cognitive processes enabling adaptive behaviors in humans and other animals is short-term memory (STM), i.e., the temporary retention of behaviorally-relevant information in the absence of direct stimulation (Goldman-Rakic, 1995). In contrast to the sizable literature describing visual STM and its neural substrates, relatively few studies have investigated auditory STM at the behavioral or neuronal levels. This central function of the auditory system is fundamental to vital behaviors such as conspecific communication. Many studies have reported that significant proportions of PFC neurons exhibit sustained changes in firing rates (often elevated but sometimes suppressed) during the retention phase of STM tasks (e.g., Fuster and Alexander, 1971; Miller et al, 1996; Shafi et al, 2007). When task contingencies require the subject to identify whether a test stimulus matches a prior sample stimulus, many PFC neurons exhibit significantly enhanced firing rates when a match is detected, whereas other cells exhibit significant match suppression (e.g., Miller et al, 1996)
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